This link (
http://www.cambridgeincolour.com/tutorials/camera-autofocus.htm
) stating that ( ... the central AF sensor is almost always the most accurate, for off-center subjects it is often best to first use this sensor to achieve a focus lock (before recomposing the frame....) .... but, what is the allowable tolerance between the Center & off center focus points .. i.e, what is the limit beyond which we can say that there are a focusing issue @ the off center focusing sensors ? ..From my opinion, finding an answer of this question may put a limit to the discussion i see regarding D800 focusing issue....Thanks